This invention relates to polymers suitable as the base resin in chemically amplified positive resist compositions used for micropatterning in a process for the fabrication of semiconductor devices. It also relates to chemically amplified positive resist compositions adapted for exposure to high-energy radiation such as deep-UV, KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), electron beams or x-rays and a process for forming a pattern.
While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, the commonly used light exposure technology is approaching the essential limit of resolution determined by the light source wavelength. For the light exposure using g-line (436 nm) or i-line (365 nm), a pattern rule of about 0.5 xcexcm is thought to be the limit. The LSI fabricated using such light exposure has a maximum degree of integration corresponding to 16 M-bit dynamic random access memory (DRAM). However, the laboratory fabrication of LSI already reached this stage, and the development of a further micropatterning technology is in urgent demand.
One means for reducing the pattern size is to reduce the wavelength of exposure light used in forming a resist pattern. For the mass production process of 256 M-bit DRAM (processing size up to 0.25 xcexcm), it is now under intensive consideration to replace i-line (365 nm) as the exposure light source by KrF excimer laser light of a shorter wavelength of 248 nm. However, for the fabrication of DRAM with a degree of integration of 1 G or more requiring a finer patterning technology (processing size up to 0.2 xcexcm), a shorter wavelength light source is required, and in particular, photolithography using ArF excimer laser light (193 nm) is now under investigation.
Since H. Ito, G. C. Willson et al of IBM proposed a chemically amplified positive resist composition comprising a resin in the form of polyhydroxystyrene having hydroxyl groups blocked with tert-butoxycarbonyloxy (tBOC) groups, that is, poly(4-t-butoxycarbonyloxystyrene) (PBOCST) and a photoacid generator in the form of an onium salt, a number of resist compositions having a high sensitivity and resolution have been developed. These chemically amplified positive resist compositions all have a high sensitivity and resolution, but are difficult to form fine patterns with a high aspect ratio because the patterns"" strength is low.
A number of chemically amplified positive resist compositions using the above-mentioned polyhydroxystyrene as the base resin and having sensitivity to deep-UV, electron beams and x-rays are known in the art. These resist compositions, however, rely on the single-layer resist method although the bi-layer resist method is advantageous in forming a pattern with a high aspect ratio on a stepped substrate. These resist compositions are not yet practically acceptable because of the outstanding problems of substrate steps, light reflection from substrates, and difficulty of forming high-aspect ratio patterns.
As is known in the art, the bi-layer resist method is advantageous in forming a high-aspect ratio pattern on a stepped substrate. It is also known that in order to develop a bi-layer resist film with a common alkaline developer, high molecular weight silicone compounds having hydrophilic groups such as hydroxyl and carboxyl groups must be used.
Among silicone base chemically amplified positive resist compositions, recently proposed were those compositions comprising a base resin in the form of polyhydroxybenzylsilsesquioxane, which is a stable alkali-soluble silicone polymer, in which some phenolic hydroxyl groups are blocked with tBOC groups, in combination with a photoacid generator (see JP-A 7-118651 and SPIE vol. 1925 (1993), 377). Also JP-A 9-110938 discloses a silicone-containing polymer using a silicon-containing acrylic monomer.
The silicon-containing polymer of the acrylic pendant type has the drawback that its resistance to dry etching with oxygen plasma is weak as compared with The silsesquioxane polymer. A low silicon content accounts for this weak dry etching resistance. The silicon-containing polymer of the siloxane pendant type has the drawback that it is repellent to developer and less wettable therewith. Then SPIE vol. 3678, pp. 214, 241 and 562 describes a polymer containing a monomer of the trisilane or tetrasilane pendant type having an increased silicon content and a silicon-containing substituent which can be eliminated with acid. However, since silane compounds of at least disilane exhibit strong absorption at the wavelength of ArF excimer laser, an increased introduction of such silanes undesirably leads to a lower transmittance. Besides, an attempt of introducing silicon into acid labile groups is reported in SPIE vol. 3678, p. 420. Because of a low acid elimination ability, there are drawbacks including low environmental stability and a T-top profile.
An object of the invention is to provide a novel polymer which is useful as the base polymer in a chemically amplified positive resist composition having a high sensitivity and high resolution, especially suitable as a material for use in the bi-layer resist method adapted to form a high-aspect ratio pattern, and capable of forming a pattern having improved heat resistance. Another object of the invention is to provide a chemically amplified positive resist composition comprising the polymer as the base resin, and a method for forming a pattern using the same.
We have found that by incorporating silicon-containing substituent groups of the general formula (1) to be shown below, the silicon content of a polymer can be increased to an effective level to prevent the transmittance of ArF excimer laser light from lowering. The silicon-containing substituent group of formula (1) functions as an acid-eliminatable substituent group by substituting for the lo hydroxyl group on a carboxylic acid, alcohol or phenol, and especially the hydroxyl group of a phenol or carboxyl group as shown by the general formula (2) to (5) to be shown below. This substituent group has so high an acid eliminating ability that the environmental stability following exposure is improved and a T-top profile is thus precluded.
In a first aspect, the invention provides a polymer having silicon-containing groups of the general formula (1): 
Herein R1 to R4 each are independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, or R1 and R2, taken together, may form an aliphatic hydrocarbon ring in which xe2x80x94CH2xe2x80x94 may be substituted with a xe2x80x94Si(R8)2xe2x80x94 group, and R3 and R4, taken together, may form an aliphatic hydrocarbon ring in which xe2x80x94CH2xe2x80x94 may be substituted with a xe2x80x94Si(R8)2xe2x80x94 group. R5 to R7 each are independently a straight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atoms or aryl group of 6 to 20 carbon atoms. R8 is independently a straight or branched alkyl group of 1 to 4 carbon atoms, and m is 1 or 2.
Preferably, hydrogen atoms of hydroxyl groups on a carboxylic acid, alcohol or phenol are substituted with the silicon-containing groups of the general formula (1).
A preferred embodiment of the invention provides a polymer comprising recurring units of one of the general formulae (2) to (5). 
Herein R1 to R7 and m are as defined above. R9 is hydrogen, a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, or CH2CO2R12. R10 is hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms. R11 is a straight, branched or cyclic alkylene group of 1 to 10 carbon atoms. R12 is hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, n is a number of 0 to 5, p is a number of 1 to 5, each of q and r is 0 or 1.
In a second aspect, the invention provides a chemically amplified positive resist composition comprising (A) the polymer defined above, (B) a photoacid generator, and (C) an organic solvent. Also contemplated herein is a chemically amplified positive resist composition comprising (A) the polymer defined above, (B) a photoacid generator, (C) an organic solvent, and (D) a dissolution rate inhibitor having an acid labile group. The resist composition may further include (E) a basic compound.
In a third aspect, the invention provides a process for forming a pattern, comprising the steps of applying the positive resist composition onto an organic film on a substrate to form a coating; prebaking the coating to form a resist film; exposing the resist film in a pattern circuit region to radiation; post-exposure baking the resist film; developing the resist film with an aqueous alkaline solution to dissolve away the exposed area, thereby forming a resist pattern; and processing the organic film with an oxygen plasma generated by a dry etching apparatus.
Polymer
The polymer or high molecular weight compound of the invention contains silicon-containing groups of the following general formula (1). 
Specifically, the inventive polymer has silicon-containing acid labile groups which exert the xcex2-cation stabilizing effect of silicon substitution. These groups advantageously have an improved acid elimination ability and prevent the development of a T-top profile. Since silicon atoms are separated by carbon atoms, the formation of a disilane bond is precluded, eliminating the risk of lowering the transmittance to ArF laser light.
In formula (1), R1 to R4, which may be the same or different, are independently selected from hydrogen and straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 6 carbon atoms. Examples of suitable straight, branched or cyclic alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, cyclopentyl, hexyl, octyl, decyl, and dodecyl. Alternatively, a pair of R1 and R2 or a pair of R3 and R4, taken together with the carbon atom to which they are bonded, may form an aliphatic hydrocarbon ring having 4 to 20 carbon atoms, preferably 6 to 15 carbon atoms, and more preferably 6 to 10 carbon atoms. In this case, each of R1 and R2 or each of R3 and R4 may be a straight, branched or cyclic alkylene group represented by xe2x80x94(CH2)xxe2x80x94 wherein x is selected so as to form an aliphatic hydrocarbon ring having a carbon number in the above range. Some or all of the xe2x80x94CH2xe2x80x94 groups may be substituted with xe2x80x94Si(R8)2xe2x80x94 groups wherein R8 is independently a straight or branched alkyl group of 1 to 4 carbon atoms.
R5 to R7, which may be the same or different, are independently selected from straight, branched or cyclic alkyl or fluorinated alkyl groups of 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 6 carbon atoms, and aryl groups of 6 to 20 carbon atoms, preferably 6 to 16 carbon atoms, and more preferably 6 to 12 carbon atoms. Exemplary alkyl groups are as enumerated above. Suitable fluorinated alkyl groups include the foregoing alkyl groups in which some or all of the hydrogen atoms are replaced by fluorine atoms, for example, difluoromethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoropropyl, 2,2,3,3-tetrafluoropropyl and 2,2,3,3,3-pentafluoropropyl. Examples of suitable aryl groups include phenyl, tolyl, xylyl and naphthyl. The letter m is 1 or 2.
Preferably, the silicon-containing groups of the general formula (1) are included as having substituted for hydrogen atoms of hydroxyl groups on a carboxylic acid, alcohol or phenol. In this regard, the polymer of the invention is preferably defined as comprising recurring units of any one of the general formulae (2) to (5): 
Herein R1 to R7 are as defined above; R9 is hydrogen, a straight, branched or cyclic C1-20 alkyl group, or CH2CO2R12; R10 is hydrogen or a straight, branched or cyclic C1-20 alkyl group; R11 is a straight, branched or cyclic C1-10 alkylene group; R12 is hydrogen or a straight, branched or cyclic C1-20 alkyl group; m is 1 or 2, n is a number of 0 to 5, p is a number of 1 to 5, each of q and r is 0 or 1.
Examples of the C1-20 alkyl group are as enumerated above, with those groups having 1 to 15 carbon atoms, especially 1 to 6 carbon atoms being preferred. Examples of C1-10 alkylene groups include methylene, ethylene, propylene, butylene, pentylene, cyclopentylene, hexylene, cyclohexylene and octylene, with those groups having 1 to 6 carbon atoms, especially 1 to 3 carbon atoms being preferred.
Illustrative examples of the recurring units having silicon-containing acid labile groups of formulae (2) through (5) are given below. It is noted that Me is methyl and Et is ethyl. 
The silicon-containing polymer of the invention, which includes recurring units having silicon-containing substituent groups of acid-eliminatable nature, may further include additional recurring units having acid-eliminatable substituent groups for the purpose of enhancing the contrast. Like the silicon-containing acid-eliminatable substituent groups, these groups are preferably incorporated as having substituted for hydrogen atoms of hydroxyl groups on a carboxylic acid, alcohol or phenol. Thus the additional recurring units are preferably any one of the following units. 
Herein Re is an acid-eliminatable substituent group, R9, R10, R11, n and r are as defined above.
The acid-eliminatable substituent groups, also referred to as acid labile groups, may be selected from a variety of such groups, and preferably from among groups of the following formulae (26) and (27), tertiary C4-40 alkyl groups of the following formula (28), and oxoalkyl groups of 4 to 20 carbon atoms. 
In formula (26), R13 is a tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group of formula (28). Exemplary tertiary alkyl groups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl, 1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and 2-methyl-2-adamantyl. Exemplary oxoalkyl groups are 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and 5-methyl-5-oxooxolan-4-yl. Letter xe2x80x9caxe2x80x9d is an integer of 0 to 6.
In formula (27), R14 and R15 are hydrogen or straight, branched or cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms. Exemplary alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, and n-octyl. R16 is a monovalent hydrocarbon group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may contain a hetero atom such as oxygen, examples of which include unsubstituted straight, branched or cyclic alkyl groups and straight, branched or cyclic alkyl groups in which some hydrogen atoms are replaced by hydroxyl, alkoxy, oxo, amino, alkylamino or the like. Illustrative examples are the substituted alkyl groups shown below. 
A pair of R14 and R15, R14 and R16, or R15 and R16 may form a ring. Each of R14, R15 and R16 is a straight or branched alkylene group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms when they form a ring.
Examples of the acid labile groups of formula (26) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl, 1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl, 1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl, 1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl, 2-tetrahydropyranyloxycarbonylmethyl, and 2-tetrahydrofuranyloxycarbonylmethyl groups.
Of the acid labile groups of formula (27), the straight and branched ones are exemplified by the following groups. 
Of the acid labile groups of formula (27), the cyclic ones are, for example, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl, tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl. Preferred among the groups of formula (27) are ethoxyethyl, butoxyethyl and ethoxypropyl.
In formula (28), R17, R18 and R19 are independently monovalent hydrocarbon groups, for example, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, which may contain a hetero atom such as oxygen, sulfur, nitrogen or fluorine. A pair of R17 and R18, a pair of R17 and R19, or a pair of R18 and R19, taken together, may form a ring.
Examples of the tertiary alkyl group represented by formula (28) include tert-butyl, triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl, 1-ethylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, and tert-amyl.
Other illustrative examples of the tertiary alkyl group are given below as formulae (35) through (50). 
Herein, R20 and R21 each are a straight, branched or cyclic alkyl group of 1 to 6 carbon atoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclopentyl or cyclohexyl. R22 is hydrogen, a monovalent C1-6 hydrocarbon group which may contain a hetero atom or a monovalent C1-6 hydrocarbon group which may be separated by a hetero atom, with the hydrocarbon being typically alkyl. The hetero atom is an oxygen, sulfur or nitrogen atom, which is contained or intervenes in the form of xe2x80x94OH, xe2x80x94OR, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94S(xe2x95x90O)xe2x80x94, xe2x80x94NH2, xe2x80x94NHR, xe2x80x94NR2, xe2x80x94NHxe2x80x94, or xe2x80x94NRxe2x80x94 wherein R is an alkyl group of 1 to 20 carbon atoms, and especially 1 to 16 carbon atoms.
R23 is hydrogen or an alkyl, hydroxyalkyl, alkoxy or alkoxyalkyl group of 1 to 20 carbon atoms, especially 1 to 16 carbon atoms, which may be straight, branched or cyclic. Illustrative examples include methyl, hydroxymethyl, ethyl, hydroxyethyl, propyl, isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, methoxy, methoxymethoxy, ethoxy, and tert-butoxy.
The oxoalkyl groups of 4 to 20 carbon atoms include 3-oxocyclohexyl and groups of the following formulae. 
For improving adhesion, the polymer may additionally include recurring units of at least one type containing a hydrophilic substituent group such as anhydride, ester (lactone), carbonate, alcohol, amide or ketone, which units are enumerated below. 
Herein R9 and R10 are as defined above.
In the polymer, further recurring units can be incorporated for the purpose of increasing the silicon content of the polymer to enhance its resistance to oxygen plasma etching. Examples of further recurring units are given below. 
Herein R9 is as defined above and Me is methyl.
The polymer is prepared in a conventional manner by furnishing predetermined amounts of a monomer having a silicon-containing group of formula (1), preferably a monomer or monomers capable of forming units of the formulae (2) through (5) and optionally, a monomer or monomers capable of forming units of formulae (2A) to (5A), a monomer or monomers capable of forming units of formulae (53) to (90) and a monomer or monomers capable of forming units of formulae (Si-1) to (Si-5), mixing the monomers in a solvent, adding a catalyst, and effecting polymerization reaction while heating or cooling if necessary. The polymerization reaction depends on the type of initiator (or catalyst), trigger means (light, heat, radiation or plasma), and polymerization conditions (including temperature, pressure, concentration, solvent and additive). Commonly used for the preparation of the inventive polymer are a radical copolymerization mode utilizing a radical of 2,2xe2x80x2-azobis-isobutyronitrile (AIBN) etc. for initiating polymerization and an ionic polymerization (anionic polymerization) mode using alkyl lithium catalysts. In either mode, polymerization can be done in a conventional manner. It is understood that the monomers capable of forming units of formulae (2) to (5) can be synthesized by the procedure described in Synthesis Example 1 or analogous procedures.
The polymer of the invention can be represented by the following formula.
xe2x80x94U1axe2x80x94U2bxe2x80x94U3cxe2x80x94U4dxe2x80x94
Herein U1 stands for recurring units having a silicon-containing group of formula (1), preferably recurring units of formulae (2) to (5), and especially recurring units of formulae (6) to (25); U2 stands for recurring units of formulae (2A) to (5A); U3 stands for recurring units of formulae (53) to (90); and U4 stands for recurring units of formulae (Si-1) to (Si-5). The letters xe2x80x9caxe2x80x9d to xe2x80x9cdxe2x80x9d are numbers satisfying 0 less than axe2x89xa61, 0xe2x89xa6b less than 1, 0xe2x89xa6c less than 1, 0xe2x89xa6d less than 1, and a+b+c+d=1. Preferably xe2x80x9caxe2x80x9d is from more than 0 to 0.9, more preferably from 0.2 to 0.8, xe2x80x9cbxe2x80x9d is from 0 to 0.5, more preferably from 0 to 0.3, xe2x80x9ccxe2x80x9d is from 0 to 0.8, more preferably from 0.1 to 0.6, and xe2x80x9cdxe2x80x9d is from 0 to 0.5, more preferably from 0 to 0.3.
The polymer preferably has a weight average molecular weight of about 1,000 to about 500,000, and especially about 3,000 to about 100,000.
Resist Composition
The polymer of the invention is suitable as a base resin in a resist composition. Thus the invention provides a resist composition comprising the above-described polymer. More specifically, the resist composition is defined herein as comprising (A) the above-described polymer as a base resin, (B) a photoacid generator, (C) an organic solvent, and optionally (D) a dissolution rate inhibitor having an acid labile group, (E) a basic compound and other components.
Organic Solvent (C)
The organic solvent used herein may be any organic solvent in which the base resin (the inventive polymer), photoacid generator, dissolution rate inhibitor and other components are soluble. Illustrative, non-limiting, examples of the organic solvent include ketones such as cyclohexanone and methyl-2-n-amylketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; and esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate. These solvents may be used alone or in combinations of two or more thereof. Of the above organic solvents, it is recommended to use diethylene glycol dimethyl ether, 1-ethoxy-2-propanol and ethyl lactate because the photoacid generator is most soluble therein, propylene glycol monomethyl ether acetate because it is a safe solvent, or a mixture thereof.
Photoacid Generator (B)
Suitable examples of the photoacid generator (B) include onium salts of formula (91) below, diazomethane derivatives of formula (92) below, glyoxime derivatives of formula (93) below, xcex2-ketosulfone derivatives, disulfone derivatives, nitrobenzylsulfonate derivatives, sulfonic acid ester derivatives, and imidoyl sulfonate derivatives.
(R24)bM+Kxe2x88x92xe2x80x83xe2x80x83(91)
In the formula, R24 is a straight, branched or cyclic alkyl of 1 to 12 carbon atoms, an aryl of 6 to 12 carbon atoms, or an aralkyl of 7 to 12 carbon atoms; M+ is iodonium or sulfonium; Kxe2x88x92 is a non-nucleophilic counter-ion; and the letter b is 2 or 3.
Illustrative examples of alkyl groups represented by R24 include methyl, ethyl, propyl, butyl, cyclohexyl, 2-oxocyclohexyl, norbornyl, and adamantyl. Exemplary aryl groups include phenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary aralkyl groups include benzyl and phenethyl. Examples of the non-nucleophilic counter-ion represented by Kxe2x88x92 include halide ions such as chloride and bromide; fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; and alkylsulfonate ions such as mesylate and butanesulfonate. 
In the formula, R25 and R26 are straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms.
Illustrative examples of alkyl groups represented by R25 and R26 include methyl, ethyl, propyl, butyl, amyl, cyclopentyl, cyclohexyl, norbornyl, and adamantyl. Exemplary halogenated alkyl groups include trifluoromethyl, 1,1,1-trifluoroethyl, 1,1,1-trichloroethyl, and nonafluorobutyl. Exemplary aryl groups include phenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary halogenated aryl groups include fluorobenzene, chlorobenzene, and 1,2,3,4,5-pentafluorobenzene. Exemplary aralkyl groups include benzyl and phenethyl. 
In the formula, R27, R28, and R29 are straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 12 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms. R28 and R29 may together form a cyclic structure with the proviso that if they form a cyclic structure, each is a straight or branched alkylene group of 1 to 6 carbon atoms.
The alkyl, halogenated alkyl, aryl, halogenated aryl, and aralkyl groups represented by R27, R28, and R29 are exemplified by the same groups mentioned above for R25 and R26. Examples of alkylene groups represented by R28 and R29 include methylene, ethylene, propylene, butylene, and hexylene.
Illustrative examples of the photoacid generator include:
onium salts such as diphenyliodonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)phenyliodonium trifluoromethanesulfonate, diphenyliodonium p-toluenesulfonate, (p-tert-butoxyphenyl)phenyliodonium p-toluenesulfonate, triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate, triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfonium butanesulfonate, trimethylsulfonium trifluoromethanesulfonate, trimethylsulfonium p-toluenesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-toluenesulfonate, dimethylphenylsulfonium trifluoromethanesulfonate, dimethylphenylsulfonium p-toluenesulfonate, dicyclohexylphenylsulfonium trifluoromethanesulfonate, and dicyclohexylphenylsulfonium p-toluenesulfonate;
diazomethane derivatives such as bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(xylenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)diazomethane, bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane, bis(isoamylsulfonyl)diazomethane, bis(secamylsulfonyl)diazomethane, bis(tert-amylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-butylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-amylsulfonyl)diazomethane, and 1-tert-amylsulfonyl-1-(tert-butylsulfonyl)diazomethane;
glyoxime derivatives such as bis-O-(p-toluenesulfonyl)-xcex1-dimethylglyoxime, bis-O-(p-toluenesulfonyl)-xcex1-diphenylglyoxime, bis-O-(p-toluenesulfonyl)-xcex1-dicyclohexylglyoxime, bis-O-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime, bis-O-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, bis-O-(n-butanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(n-butanesulfonyl)-xcex1-diphenylglyoxime, bis-O-(n-butanesulfonyl)-xcex1-dicyclohexylglyoxime, bis-O-(n-butanesulfonyl)-2,3-pentanedioneglyoxime, bis-O-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, bis-O-(methanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(trifluoromethanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(1,1,1-trifluoroethanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(tert-butanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(perfluorooctanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(cyclohexanesulfonyl)-xcex1-dimethylglyoxime, bis-O-(benzenesulfonyl)-xcex1-dimethylglyoxime, bis-O-(p-fluorobenzenesulfonyl)-xcex1-dimethylglyoxime, bis-O-(p-tert-butylbenzenesulfonyl)-xcex1-dimethylglyoxime, bis-O-(xylenesulfonyl)-xcex1-dimethylglyoxime, and bis-O-(camphorsulfonyl)-xcex1-dimethylglyoxime;
xcex2-ketosulfone derivatives such as 2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane and 2-isopropylcarbonyl-2-(p-toluenesulfonyl)propane;
disulfone derivatives such as diphenyl disulfone and dicyclohexyl disulfone;
nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzyl p-toluenesulfonate and 2,4-dinitrobenzyl p-toluenesulfonate;
sulfonic acid ester derivatives such as 1,2,3-tris(methanesulfonyloxy)benzene, 1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and 1,2,3-tris(p-toluenesulfonyloxy)benzene; and
imidoyl sulfonate derivatives such as phthalimidoyl triflate, phthalimidoyl tosylate, 5-norbornene-2,3-dicarboxyimidoyl triflate, 5-norbornene-2,3-dicarboxyimidoyl tosylate, and 5-norbornene-2,3-dicarboxyimidoyl n-butylsulfonate.
Preferred among these photoacid generators are onium salts such as triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, and tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate; diazomethane derivatives such as bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)diazomethane, and bis(tert-butylsulfonyl)diazomethane; and glyoxime derivatives such as bis-O-(p-toluenesulfonyl)-xcex1-dimethylglyoxime and bis-O-(n-butanesulfonyl)-xcex1-dimethylglyoxime. These photoacid generators may be used singly or in combinations of two or more thereof. Onium salts are effective for improving rectangularity, while diazomethane derivatives and glyoxime derivatives are effective for reducing standing waves. The combination of an onium salt with a diazomethane or a glyoxime derivative allows for fine adjustment of the profile.
The photoacid generator is added in an amount of 0.2 to 15 parts by weight, and especially 0.5 to 8 parts by weight, per 100 parts by weight of all the base resins. At less than 0.2 part, the amount of acid generated during exposure would be too low and the sensitivity and resolution are poor, whereas the addition of more than 15 parts would lower the transmittance of the resist and results in a poor resolution.
Dissolution Rate Inhibitor (D)
To the resist composition, a dissolution rate inhibitor may be added. The dissolution rate inhibitor is a compound having on the molecule at least two phenolic hydroxyl groups, in which an average of from 0 to 100 mol % of all the hydrogen atoms on the phenolic hydroxyl groups are replaced with acid labile groups or a compound having on the molecule at least one carboxyl group, in which an average of 10 to 100 mol % of all the hydrogen atoms on the carboxyl groups are replaced with silicon-containing groups of formula (1), both the compounds having an average molecular weight within a range of 100 to 1,000, and preferably 150 to 800.
The degree of substitution of the hydrogen atoms on the phenolic hydroxyl groups with acid labile groups is on average at least 0 mol %, and preferably at least 30 mol %, of all the phenolic hydroxyl groups. The upper limit is 100 mol %, and preferably 80 mol %. The degree of substitution of the hydrogen atoms on the carboxyl groups with acid labile groups is on average at least 50 mol %, and preferably at least 70 mol %, of all the carboxyl groups, with the upper limit being 100 mol %.
Preferable examples of such compounds having two or more phenolic hydroxyl groups or compounds having at least one carboxyl group include those of formulas (D1) to (D14) below. 
In these formulas, R101 and R102 are each hydrogen or a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms; R103 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or xe2x80x94(R107)hxe2x80x94COOH; R104 is xe2x80x94(CH2)ixe2x80x94 (where i=2 to 10), an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R105 is an alkylene of 1 to 10 carbon atoms, an arylene of 6 to 10 carbon atoms, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R106 is hydrogen, a straight or branched alkyl or alkenyl of 1 to 8 carbon atoms, or a hydroxyl-substituted phenyl or naphthyl; R107 is a straight or branched alkylene of 1 to 10 carbon atoms; R108 is hydrogen or hydroxyl; the letter j is an integer from 0 to 5; u and h are each 0 or 1; s1, t1, s2, t2, s3, and t3 are each numbers which satisfy s1+t1=8, s2+t2=5, and s3+t3=4, and are such that each phenyl skeleton has at least one hydroxyl group; and xcex1 is a number such that the compounds of formula (D8) or (D9) have a molecular weight of from 100 to 1,000.
In the above formulas, suitable examples of R101 and R102 include hydrogen, methyl, ethyl, butyl, propyl, ethynyl, and cyclohexyl; suitable examples of R103 include the same groups as for R101 and R102, as well as xe2x80x94COOH and xe2x80x94CH2COOH; suitable examples of R104 include ethylene, phenylene, carbonyl, sulfonyl, oxygen, and sulfur; suitable examples of R105 include methylene as well as the same groups as for R104; and suitable examples of R106 include hydrogen, methyl, ethyl, butyl, propyl, ethynyl, cyclohexyl, and hydroxyl-substituted phenyl or naphthyl.
Basic Compound (E)
The basic compound (E) is preferably a compound capable of suppressing the rate of diffusion when the acid generated by the photoacid generator diffuses within the resist film. The inclusion of this type of basic compound holds down the rate of acid diffusion within the resist film, resulting in better resolution. In addition, it suppresses changes in sensitivity following exposure, thus reducing substrate and environment dependence, as well as improving the exposure latitude and the pattern profile. (See, for example, JP-A 5-232706, JP-A 5-249683, JP-A 5-158239, JP-A 5-249662, JP-A 5-257282, JP-A 5-289322, and JP-A 5-289340).
Examples of suitable basic compounds include primary, secondary, and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, carboxyl group-bearing nitrogenous compounds, sulfonyl group-bearing nitrogenous compounds, hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, alcoholic nitrogenous compounds, amide derivatives, and imide derivatives. Of these, aliphatic amines are especially preferred.
Examples of suitable primary aliphatic amines include ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, iso-butylamine, sec-butylamine, tert-butylamine, pentylamine, tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine, cetylamine, methylenediamine, ethylenediamine, and tetraethylenepentamine. Examples of suitable secondary aliphatic amines include dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, di-n-butylamine, di-iso-butylamine, di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine, dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, didodecylamine, dicetylamine, N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, and N,N-dimethyltetraethylenepentamine. Examples of suitable tertiary aliphatic amines include trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine, tri-iso-butylamine, tri-sec-butylamine, tripentylamine, tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, tridodecylamine, tricetylamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylmethylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, and N,N,Nxe2x80x2,Nxe2x80x2-tetramethyltetraethylenepentamine.
Examples of suitable mixed amines include dimethylethylamine, methylethylpropylamine, benzylamine, phenethylamine, and benzyldimethylamine. Examples of suitable aromatic and heterocyclic amines include aniline derivatives (e.g., aniline, N-methylaniline, N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline, ethylaniline, propylaniline, trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, and N,N-dimethyltoluidine), diphenyl(p-tolyl)amine, methyldiphenylamine, triphenylamine, phenylenediamine, naphthylamine, diaminonaphthalene, pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole, 2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazole derivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g., thiazole and isothiazole), imidazole derivatives (e.g., imidazole, 4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazole derivatives, furazan derivatives, pyrroline derivatives (e.g., pyrroline and 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine, N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone), imidazoline derivatives, imidazolidine derivatives, pyridine derivatives (e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine, butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine, trimethylpyridine, triethylpyridine, phenylpyridine, 3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine, benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine, 1-methyl-2-pyridine, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine, 2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine), pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives, pyrazoline derivatives, pyrazolidine derivatives, piperidine derivatives, piperazine derivatives, morpholine derivatives, indole derivatives, isoindole derivatives, 1H-indazole derivatives, indoline derivatives, quinoline derivatives (e.g., quinoline and 3-quinolinecarbonitrile), isoquinoline derivatives, cinnoline derivatives, quinazoline derivatives, quinoxaline derivatives, phthalazine derivatives, purine derivatives, pteridine derivatives, carbazole derivatives, phenanthridine derivatives, acridine derivatives, phenazine derivatives, 1,10-phenanthroline derivatives, adenine derivatives, adenosine derivatives, guanine derivatives, guanosine derivatives, uracil derivatives, and uridine derivatives.
Examples of suitable carboxyl group-bearing nitrogenous compounds include aminobenzoic acid, indolecarboxylic acid, and amino acid derivatives (e.g. nicotinic acid, alanine, alginine, aspartic acid, glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine, methionine, phenylalanine, threonine, lysine, 3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples of suitable sulfonyl group-bearing nitrogenous compounds include 3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples of suitable hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, and alcoholic nitrogenous compounds include 2-hydroxypyridine, aminocresol, 2,4-quinolinediol, 3-indolemethanol hydrate, monoethanolamine, diethanolamine, triethanolamine, N-ethyldiethanolamine, N,N-diethylethanolamine, triisopropanolamine, 2,2xe2x80x2-iminodiethanol, 2-aminoethanol, 3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine, 2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine, 1-[2-(2-hydroxyethoxy)ethyl]-piperazine, piperidine ethanol, 1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone, 3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol, 8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidine ethanol, 1-aziridine ethanol, N-(2-hydroxyethyl)phthalimide, and N-(2-hydroxyethyl)isonicotinamide. Examples of suitable amide derivatives include formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, and benzamide. Suitable imide derivatives include phthalimide, succinimide, and maleimide.
In addition, basic compounds of the following general formulas (94) and (95) may also be included. 
In the formulas, R201, R202, R203, R207 and R208 independently straight, branched or cyclic alkylenes of 1 to 20 carbon atoms; R204, R205, R206, R209 and R210 are hydrogen, alkyls of 1 to 20 carbon atoms, or amino; R204 and R205, R205 and R206, R204 and R206, R204 with R205 and R206, and R209 and R210 may bond together to form rings; and X, Y and Z are each integers from 0 to 20, with the proviso that hydrogen is excluded from R204, R205, R206, R209 and R210 when X, Y and Z are equal to 0.
The alkylene groups represented by R201, R202, R203, R207 and R208 preferably have 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, and most preferably 1 to 8 carbon atoms. Examples include methylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene, n-pentylene, isopentylene, hexylene, nonylene, decylene, cyclopentylene, and cyclohexylene.
The alkyl groups represented by R204, R205, R206, R209 and R210 preferably have 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms, and may be straight, branched or cyclic. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, hexyl, nonyl, decyl, dodecyl, tridecyl, cyclopentyl, and cyclohexyl.
Where R204 and R205, R205 and R206, R204 and R206, R204 with R205 and R206, and R209 and R210 form rings, the rings preferably have 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms, and may have branching alkyl groups of 1 to 6 carbon atoms, and especially 1 to 4 carbon atoms.
X, Y, and Z are each integers from 0 to 20, preferably from 1 to 10, and more preferably from 1 to 8.
Illustrative examples of the compounds of formulas (94) and (95) include tris{2-(methoxymethoxy)ethyl}amine, tris{2-(methoxyethoxy)ethyl}amine, tris[2-{(2-methoxyethoxy)methoxy}ethyl]amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine, tris[2-{(2-hydroxyethoxy)ethoxy}ethyl]amine, 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane, 1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane, 1-aza-12-crown-4,1-aza-15-crown-5, and 1-aza-18-crown-6. Especially preferred basic compounds are tertiary amines, aniline derivatives, pyrrolidine derivatives, pyridine derivatives, quinoline derivatives, amino acid derivatives, hydroxyl group-bearing nitrogenous compounds, hydroxyphenyl group-bearing nitrogenous compounds, alcoholic nitrogenous compounds, amide derivatives, imide derivatives, tris{2-(methoxymethoxy)ethyl}amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris[2-{(2-methoxyethoxy)methyl}ethyl]amine, and 1-aza-15-crown-5.
The above-described basic compound may be used singly or in combinations of two or more thereof, and is preferably formulated in an amount of 0.01 to 2 parts by weight, and especially 0.01 to 1 part by weight, per 100 parts by weight of all the base resins. At less than 0.01 part, the desired effects of the basic compound would not be apparent, while the use of more than 2 parts would result in too low a sensitivity.
The resist composition of the invention may include optional ingredients, typically a surfactant which is commonly used for improving the coating characteristics. Optional ingredients may be added in conventional amounts so long as this does not compromise the objects of the invention.
Nonionic surfactants are preferred, examples of which include perfluoroalkylpolyoxyethylene ethanols, fluorinated alkyl esters, perfluoroalkylamine oxides, and fluorinated organosiloxane compounds. Useful surfactants are commercially available under the trade names Florade FC-430 and FC-431 from Sumitomo 3M Co., Ltd., Surflon S-141, S-145, S-381 and S-383 from Asahi Glass Co., Ltd., Unidyne DS-401, DS-403 and DS-451 from Daikin Industry Co., Ltd., Megaface F-8151, F-171, F-172, F-173 and F-177 from Dai-Nippon Ink and Chemicals, Inc., and X-70-092 and X-70-093 from Shin-Etsu Chemical Co., Ltd. Preferred surfactants are Florade FC-430 from Sumitomo 3M K.K. and X-70-093 from Shin-Etsu Chemical Co., Ltd.
Pattern formation using the resist composition of the invention may be carried out by a known lithographic technique. For example, the resist composition is applied onto an organic film on a substrate such as a novolac film of about 0.1 to 10.0 xcexcm thick on a silicon wafer by spin coating or the like to form a resist film having a thickness of 0.1 to 1.0 xcexcm, which is then pre-baked on a hot plate at 60 to 200xc2x0 C. for 10 seconds to 10 minutes, and preferably at 80 to 150xc2x0 C. for 30 seconds to 5 minutes. A patterning mask having the desired pattern is then placed over the resist film, and the film is exposed through the mask to an electron beam or high-energy radiation having a wavelength of up to 300 nm such as deep-UV, an excimer laser, or x-rays in a dose of about 1 to 200 mJ/cm2, and preferably about 10 to 100 mJ/cm2, then post-exposure baked (PEB) on a hot plate at 60 to 150xc2x0 C. for 10 seconds to 5 minutes, and preferably at 80 to 130xc2x0 C. for 30 seconds to 3 minutes. Development is then carried out using as the developer an aqueous alkali solution, such as a 0.1 to 5% (preferably 2 to 3%) aqueous solution of tetramethylammonium hydroxide (TMAH), this being done by a conventional method such as dipping, puddling, or spraying for a period of 10 seconds to 3 minutes, and preferably 30 seconds to 2 minutes. These steps result in the formation of the desired pattern on the substrate. Of the various types of high-energy radiation that may be used, the resist composition of the invention is best suited to micropattern formation with, in particular, deep-UV rays and excimer laser light having a wavelength of 254 to 120 nm, especially KrF excimer laer of 248 nm or ArF excimer laser of 193 nm, x-rays, and an electron beam. The desired pattern may not be obtainable outside the upper and lower limits of the above range.
In the developing step, the exposed area of the resist film is dissolved away until the underlying organic film is exposed. Then the exposed area of the organic film is conventionally processed with an oxygen plasma generated by a dry etching apparatus.
The resist composition comprising the polymer of the invention as a base resin is sensitive to high-energy radiation and has excellent sensitivity and resolution at a wavelength of less than 300 nm, and high resistance to oxygen plasma etching. Because of these advantages, the resist composition is suited for bi-layer resist and easily forms a finely defined pattern having sidewalls perpendicular to the substrate. The resist composition lends itself to micropatterning for the fabrication of VLSIs.